The woman has an extremely drug-resistant form of the disease, which is impervious to most TB drugs. Three to four cases are reported each year in the United States, on average.
Health officials in Illinois are working with the Centers for Disease Control and Prevention to find people with whom the woman may have had prolonged direct contact, in close quarters, CDC spokesman Tom Skinner said.
TB is not as easily spread as diseases like the flu or measles. But it is a dangerous illness, especially for people with weakened immune systems, and health officials are taking the situation seriously, Skinner said.
In April, the woman travelled from India to the United States, arriving at Chicago's O'Hare International Airport. She spent time in Missouri, Tennessee and Illinois before growing sick and being admitted to an isolation unit at a suburban Chicago hospital.
She is now being cared for at a National Institutes of Health hospital in Bethesda, Maryland, where she is in stable condition. The CDC did not release other details.
Tuberculosis is caused by bacteria spread from person to person through the air. It usually affects the lungs and can lead to symptoms such as chest pain and coughing up blood.
TB has been declining in the United States. But globally, each year it sickens about 9 million people and is a cause of 1.5 million deaths.